Noise suppression method for wave filter

Abstract

A noise suppression method of a wave filter used to eliminate standing wave signal interferences in the acoustic wave filter consisted by a plurality of film bulk acoustic resonators (FBARs). The method is to provide a plurality of scatterers in the structured consisted by the FBARs, thereby creating an band-gap structure due to the material characteristics difference, which consequently generates a destructive interfering effect to the transverse higher harmonics vibration within a specific operating frequency range, and ultimately decreases or even eliminates any parasitic effects. Therefore, within the operation frequency range of this band-gap structure, abnormal signals created by any transverse wave modes cannot exist. In addition, an acoustic shield can be provided by phononic crystal structures between different FBARs, thus acoustic shielding any mutual interference within the operation frequency range.

Description

FIELD OF THE INVENTION[0001]The present invention relates to a noise suppression technique, and more particularly, to a noise suppression method that forms a plurality of scatterers in the structure of film bulk acoustic resonators, thereby allowing destructive interfering effect to be applied to transverse higher harmonics vibration due to the band-gap structure generated by characteristics difference between materials used.DESCRIPTION OF THE PRIOR ART[0002]For conventional crystal wave filters used in VHF and HF bands under 300 MHz, the upper limit of operating frequency is mainly restricted by accuracy of the crystal thickness thinning process, which suppresses the rising of operating frequency. Nowadays, micro-electro-mechanical system (MEMS), combined with accurate control of sputtering film thickness, are used to obtain crystal-filer-structure alike thin Film Bulk Acoustic Resonators (FBARs), the resonant frequency of which can be raised to several GHz to tens of GHz. In recen...

AI Technical Summary

Benefits of technology

The present invention provides a noise suppression method for a wave filter that utilizes a material structural design to solve the standing wave signal interference found in conventional FBARs. The method arranges a plurality of scatterers in the FBARs, which produce a destructive interfering effect to transverse higher harmonics vibration within the operating frequency range, thus any transverse propagating acoustic waves cannot exist in the operating frequency range. The present invention can completely eliminate abnormal signals created by any transverse mode, unlike the prior art where energy of the transverse spikes is only partly reduced. The FBARs provided by the noise suppression method for a wave filter of the present invention can be constructed by air-bridge structures on a substrate or in front-side / backside etched cavity, and the scatterers can be periodically or randomly formed as cylinders or voids in the overlap of working electrodes and piezoelectric film or even in the whole piezoelectric film.

Problems solved by technology

These scatterers produce a destructive interfering effect to transverse higher harmonics vibration within the operating frequency range, thus any transverse propagating acoustic waves, whether it is the wave vector or the resonant mode thereof, cannot exist in the operating frequency range.

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